1. Field of the Invention
This invention relates to an automotive air conditioner for conditioning air in a room of an automobile. The automotive air conditioner of the present invention is effectively applied to an automobile which does not have a surplus heat source as, for example, an electric automobile.
2. Related Art
Usually, an automotive air conditioner makes use, in order to heat air, of heat from cooling water for an engine for driving an automobile. However, heating of air is performed using a heat pump when the amount of heat of cooling water for an engine is insufficient or when an automobile does not originally have engine cooling water such as an electric automobile.
For example, in an automotive air Application No. 60-219114, a flow of refrigerant is changed over by means of a four-way valve such that an inside heat exchanger is used either as an evaporator to cool air or as a condenser to heat air.
With the automotive air conditioner wherein cooling operation and heating operation are performed alternatively by changing over of a four-way valve in this manner, since the single heat exchanger changes its function immediately between a function of an evaporator and another function of a condenser, there is the possibility that, particularly when the function is changed over, a large amount of moisture may be blasted from a surface of the inside heat exchanger toward the inside of the room of the automobile.
In particular, water condensed on a surface of the inside heat exchanger during cooling operation is evaporated from the surface of the inside heat exchanger as a result of changing over to heating operation and then carried into the room of the automobile by a blower. Such blasting of a large amount of water will instantaneously fog a windshield and/or window glass. The fog will make an obstacle to a field of view in driving the automobile and is very inconvenient.
Accumulator cycles are conventionally known wherein a subcooling control valve is disposed on the downstream side of a refrigerant condenser to obtain a subcooled condition of refrigerant.
An exemplary one of subcooling control valves is disclosed, for example, in Japanese Utility Model Laid-Open Application No. Showa 55-85671 and is shown in FIG. 100. Referring to FIG. 100, the subcooling control valve 1100 includes a valve body 1103 for opening or closing a throttle section 1102 by operation of a diaphragm 1101, a regulating spring 1104 for normally biasing the valve body 1103 to open the throttle section 1102, and a temperature sensitive tube 1105 for converting a variation of temperature of refrigerant on the downstream side of a refrigerant condenser (not shown) into a variation of pressure.
The displacement of the valve body 1103 is adjusted by the balance between the pressure in the temperature sensitive tube 1105 which acts upon the upper side of the diaphragm 1101 via a capillary tube 1106 and the high pressure of the refrigerant and the biasing force of the regulating spring 1104 which both act upon the lower side of the diaphragm 1101, and the opening of the throttle section 1102 depends upon the displacement of the valve body 1103.
However, in the subcooling control valve 1100 described above, since the biasing force of the regulating spring 1104 is set in advance so that a predetermined subcooling degree (for example, 5 to 10.degree. C.) may be obtained within the refrigerant condenser, when it is tried to construct such a novel subcooling cycle as shown in FIG. 101 or 1017 using the subcooling control valve 1100, such subjects to be solved as described below are involved.
Referring first to FIG. 101, the subcooling cycle shown constitutes a heat pump cycle for an automotive air conditioner and includes a refrigerant compressor 1200, an interior condenser 1202 disposed in a duct 1201 which introduces blast air into the room of the automobile, a subcooling control valve 1100, an interior evaporator 1203 disposed in the duct 1201 on the upstream side of the interior condenser 1202, an evaporation pressure regulating valve 1204, an exterior evaporator 1205 disposed on the outside of the duct 1201, an accumulator 1206, a bypass passageway 1207 for bypassing the interior evaporator 1203 and the evaporation pressure regulating valve 1204, and a solenoid valve 1208 for opening or closing the bypass passageway 1207.
Now, if the bypass passageway 1207 is closed by the solenoid valve 1208 so that the refrigerant flowing out through the subcooling control valve 1100 is introduced into the interior evaporator 1203, then air introduced into the duct 1201 by a fan 1209 is cooled when it passes through the interior evaporator 1203, and thereafter, the air is heated when it passes through the interior condenser 1202, and then it blown out into the room of the vehicle. In this instance, when the saturation temperature of the refrigerant flowing through the interior condenser 1202 is 50.degree. C. or around it, as cool air of a temperature close to 0.degree. C. cooled by the interior evaporator 1203 is blown to the interior condenser 1202, ideally a subcooling degree of the temperature of 50.degree. C. or so can be obtained at the interior condenser 1202.
On the other hand, if the bypass passageway 1207 is opened by the solenoid valve 1208 to allow the refrigerant flowing out from the subcooling control valve 1100 to be introduced into the exterior evaporator 1205 while an internal air mode is set so that air in the automobile room of a temperature of 30.degree. C. or around it is introduced into the duct 1201, then the air introduced in the duct 1201 is blown to the interior condenser 1202 while keeping its temperature (30.degree. C.) without being cooled by the interior evaporator 1203. Consequently, only a subcooling degree of the temperature of 20.degree. C. or so to the utmost can be obtained at the interior condenser 1202.
In the meantime, the subcooling cycle shown in FIG. 102 constitutes a refrigerating cycle for an automotive air conditioner and includes an exterior evaporator 1210 on the upstream side of an interior condenser 1202, and an air mixing damper 1211 for adjusting the amount of draft air to the interior condenser 1202. When the air mixing damper 1211 is opened or closed, cooling air of the temperature of 0.degree. C. or around it cooled by an interior evaporator 1203 is blown to or not blown to the interior condenser 1202.
For example, when the air mixing damper 1211 fully opens the interior condenser 1202 (the position indicated by full lines in FIG. 102) so that cool air of the temperature of 0.degree. C. or around it is blown to the interior condenser, if the saturation temperature of the refrigerant flowing through the interior condenser 1202 is 50.degree. C. or around it, a subcooling degree of the temperature ideally of 50.degree. C. or around it can be obtained.
On the other hand, when the air mixing damper 1211 closes the interior condenser 1202 (the position indicated by chain lines in FIG. 102), cool air is not blown to the interior condenser 1202, and the interior condenser 1202 acts as a mere refrigerant passageway. Consequently, if the external air temperature (the temperature of wind blown to the exterior condenser 1210) is 30.degree. C., then while the saturation temperature of the refrigerant flowing through the exterior condenser 1201 and the interior condenser 1202 is 50.degree. C., only a subcooling degree of the temperature of 20.degree. C. or so can be obtained even if the refrigerant is cooled ideally to 30.degree. C. of the external air temperature.
Accordingly, where the biasing force of the regulating spring 1104 of the subcooling control valve 1100 is set in the subcooling cycles shown in FIGS. 101 and 102 so that the subcooling degree of 20.degree. C. may be obtained at the interior condenser 1202, the subcooling control valve 1100 tends to control the subcooling degree of 20.degree. C. even when cool wind of the temperature of 0.degree. C. or around it cooled by the interior evaporator 1203 is blown to the interior condenser 1202. Consequently, a sufficiently high subcooling degree (50.degree. C.) cannot be obtained making use of cool wind of the temperature of 0.degree. C. or around it as described hereinabove.
On the contrary, where the biasing force of the regulating spring 1104 of the subcooling control valve 1100 is set so that the subcooling degree of 50.degree. C. may be obtained at the interior condenser 1202, even when the temperature of draft air blown to the interior condenser 1202 in the refrigerating cycle shown in FIG. 101 is 30.degree. C. or around it or even when the air mixing damper 1211 in the refrigerating cycle shown in FIG. 102 closes the interior condenser 1202, the subcooling control valve 1100 tends to reduce the opening of the throttle section 1102 until the subcooling degree of 50.degree. C. is obtained at the interior condenser 1202, and consequently, the pressure on the high pressure side rises to a very high level.
In the conventional subcooling control valve 1100, the biasing force of the regulating spring 1104 is set so that a predetermined subcooling degree may be obtained in the interior condenser 1202 in this manner. Accordingly, the conventional subcooling control valve 1100 cannot cope with the construction of such a cycle wherein the temperature of air blown to the interior condenser 1202 varies over a wide range so that subcooling obtained at the interior condenser 1202 varies over a wide range (the subcooling degree cannot be controlled over a wide range), and consequently, the cycle efficiency is low.